The present invention relates generally to a rotation detection device such as that used by a digital display value adjusting device. In particular, the present invention relates to a pulse generator of a rotation detection device of a digital display value adjusting device.
In a conventional digital display value adjusting device, such as that disclosed in Japanese Patent Publication No. 60-26477, a manual input device (such as a manually rotatable stem) of a pulse generator is rotated to generate at least two pulse strings which are time-wise shifted but overlap each other. Pulse information is output by the pulse generator when there is a change in the pulse strings. A bit word of 4-bits indicating the change in the state of a pulse is obtained based on the current pulse information and the pulse information which has been output from the pulse generator prior to the current pulse information. The direction of rotation of the manual input device is determined by detecting the coincidence between the bit word and a bit word stored in advance in a fixed storage device. A digital display value is adjusted on the basis of the result of the determination.
For example, if current pulse information "00" is generated from the pulse generator and the previous pulse information is "10" the bit word will be "0010". The bit word "0010" is stored in the fixed storage device as clockwise pulse information which undergoes coincidence detection, and it is thus determined that the manual input device has been rotated in a clockwise direction. As described above, pulse information indicating the direction of rotation is stored in advance in the fixed storage device. When the pulse generator generates pulse information which coincides with the stored pulse information, the direction of rotation of the manual input device is ascertained.
A conventional pulse generator utilizing a manual input device, such as a rotary stem, may malfunction, as shown in FIG. 4 for example, when a pulse in one string is missed and is not generated because the rotation of the manual input device is unintentionally momentarily interuppted or changed. If it is assumed that the changes in the pulses at times t1 to t5 in FIG. 4 represent correct operating conditions in the case wherein the manual input device is rotated clockwise, the conventional pulse generator has stored in advance in its fixed storage device "0001", "1011", "1110" and "1000" as clockwise or up bit words, and "0010" "1011" "1101" and. "0100" as counterclockwise or down bit words. Therefore, the rotation is determined to be clockwise at times t1 to t5.
However, if for some reason one of the pulses (indicated by broken lines) is not generated, pulse information "10" generated at time t6 will result in a bit word "0010" which is determined to be a counterclockwise direction. Therefore, when this occurs, even though the manual input device continues to be rotated in the clockwise direction, the pulse generator may output a bit word that determines the rotation to be in the opposite, or counterclockwise, direction.
Further, in accordance with the conventional pulse generator, it takes time to obtain the bit word based on the current pulse information and the next previous pulse information. In addition, a fixed storage device is required for storing in advance the bit words to be checked for coincidence with the bit word thus obtained. This results in an increase in the size of the circuit, thus increasing the cost of the device.